1. Field of Invention
This invention relates to missile systems. Specifically, the present invention relates to systems for accurately determining the velocity and vertical position of a missile in flight.
2. Description of the Related Art
Missiles are designed for a variety of demanding applications ranging from explosives delivery to satellite launching applications. Such applications often require accurate missile velocity, acceleration, and position information to make in-flight steering and targeting adjustments. Such accurate kinematic information is particularly important in military applications involving low flying missiles. Slight errors in missile vertical velocity and altitude measurements will hamper the use of this information for missile functions. This results in decreased missile accuracy and lethality.
Typically, missiles used in military applications include an on-board inertial reference unit (IRU) for taking missile kinematic measurements. The IRU has a sensor that detects changes in missile inertial position accelerometers in the IRU and measure missile accelerations which are then used to compute missile velocity, and position. The current missile position and velocity are calculated with reference to an initial position and velocity, respectively. Initialization error and IRU measurement error accumulate over the flight of a missile, severely degrading missile vertical velocity and position estimates.
A system that utilizes missile radar range, i.e., distance measurements rather than IRU measurements is often used to correct error associated with missile vertical velocity estimates. In this system, radar range measurements are differentiated to obtain estimates of missile velocity. Significant error often results, however, due to radar sensor noise. Other similar systems attempt to reduce the effects of sensor noise by averaging radar range measurements before differentiation. These systems however, fail to account for missile vertical acceleration due to missile velocity and flight path angle changes. Resulting vertical velocity measurement errors are still unacceptable for some applications.
Hence, a need exists in the art for a system that accurately measures missile vertical velocity and position, that is immune to IRU initialization error, and that takes into account changes in vertical acceleration of the missile.